While you can't get in touch with the instructor, who is coordinating the course here?
Contact them, as they should have the answers.
There are some battings here in our LQS' that are specifically promoted as being for tote bags.
Sorry, but I can't think of the names ......
The concept being that they have the ability to let the bag stand up when you set it down,
rather than it slump into a puddle!
And if you want something really firm and stiff (like a board!) there are the Pellon products.
Again, sorry, but I forget what # they are.